1. Field of the Invention
The present invention relates to railway signals, particularly Light Emitting Diode (LED) searchlight signals.
Searchlight signals are used along railway tracks to convey information to the train driver, they can display three colors (red, yellow or green) out of the same lamp by placing a filter in front of it. These searchlight signals are composed of an incandescent lamp, a reflector, a lens system and three colored filters or xe2x80x9croundelsxe2x80x9d(red, yellow and green). An electromechanical three position DC motor mechanism selects the proper filter to be used. This electromechanical system is controlled by an external DC control voltage. In the absence of any control voltage, the red filter remains in front of the light beam, displaying a red aspect. If the control voltage is positive (12V), the yellow filter is moved in front of the light beam and a yellow aspect is displayed. If the control voltage is negative (xe2x88x9212V), the green lens is placed in front of the light beam, displaying a green aspect. Six external repeater contacts are also used, providing feedback information to a central control installation on which aspect is currently displayed or not displayed. These contacts are used in other stages of the signaling system.
This searchlight mechanism has been used for over a century by the railway industry but it has two major drawbacks. First, it is very expensive due to the complexity of its electromechanical and optical systems. Second, its maintenance costs are high due to the relatively short life of the incandescent lamps and the required periodic maintenance and calibration of the internal electromechanical mechanism.
The present invention uses the high reliability and long life of LEDs and the versatility of a switching power supply to create an LED searchlight signal that can be easily retrofitted into existing signal systems. This new searchlight signal features relatively low capital and operating costs, no bulb replacement and virtually no required maintenance for several years.
2. Description of the Related Art
U.S. Pat. No. 5,697,584 describes a searchlight signal using LEDs, reflector, light filters, light detection means and a linear power supply. An object of the present invention is to provide the reliability and energy efficiency of LEDs, without requiring the added complexity and expense of a reflector, light filters, light detection means or a linear power supply.
The present invention uses a printed circuit board populated by three arrays (green, red and yellow) of LEDs. The LEDs are lit by a standard color light power supply unit (PSU). As only one array of LEDs is lit at a time, an interface between the PSU and the LEDs is provided to select which LED array to couple with the PSU. External repeater contacts provide information on which aspect is displayed. This searchlight system design is failsafe in that no single failure of a component will produce a less restrictive aspect.